This research is aimed at improving our knowledge of how polycyclic hydrocarbons initiate tumours and why they show activity in some tissues in some species but are inactive in others. Specifically we wish (i) to further characterize the adducts formed when nucleic acids are modified by chrysene triol-epoxides, (ii) to compare the abilities of DNA adducts formed from chrysene diol- and triol-epoxides to cause mutations and to activate proto-oncogenes, (iii) to investigate the possibility that some polycyclic hydrocarbon metabolites cause product inactivation of cytochrome P450 enzymes involved in their further metabolism, (iv) to determine if different cytochrome P450 enzymes show differences in the stereospecificity with which they metabolize polycyclic hydrocarbons, (v) to examine the relative persistence of hydrocarbon-nucleic acid adducts in the skin and possibly in the keratinocytes of different species including man and (vi) to attempt to modify the Randerath 32-P-postlabeling assay so that it may be used to measure the total DNA modification that results when cells or tissues are treated, either in vivo or in vitro with products such as coal tar, creosote or cigarette smoke condensate that contain mixtures of a variety of unlabeled polycyclic hydrocarbons. The methods to be used include in vitro and in vivo treatment of skin and/or keratinocytes with polycyclic hydrocarbons, the isolation of nucleic acids and nucleic acid adducts by Sephadex LH20 column chromatography and hplc and their quantitation and characterization by physico-chemical methods. Cytochrome P450 enzyme activities and stereoselectivities will be measured by published methods or by methods already in use. The 32-P-postlabeling assays and proto-oncogene activation studies will be carried out by procedures currently employed in this laboratory. A better understanding of the mechanisms involved in polycyclic hydrocarbon carcinogenesis and of the reasons for tissue and species susceptibility may eventually lead to the development of strategies designed to prevent the initiation of some forms of human cancer.